Secret sounder



Feb. 21, 1939. E. P. BANCRIOFT SECRET SOUNDER Filed Nov. 24, 1936 INVENTOR E/P/W/V R BA/VC/FOFT ATTORNEY Patented Feb. 21, 1939 PATENT OFFlCE SECRET SOUNDER Erwin P. Bancroft, Brooklyn, N. Y., assignor to Postal Telegraph-Cable Company (New York), New York, N. Y., a corporation of New York Application November 24, 1936, Serial No. 112,457

10 Claims.

This invention relates to telegraph sounders and pertains more particularly to sounders of the so-called secret type.

Secret sounders for the reception of telegraph signals have been known heretofore, but have been subject to serious defects of one kind or another. Some of them have been practically non-adjustable under working conditions, limited in their range of adjustment or difficult to read. In some cases these sounders have been subject to a condition resulting in the reception of the signal in such manner that the received sound is inverted and unreadable. Furthermore, sounders in accordance with the prior art have had the disadvantage that the signal from them can be heard and read at a considerable distance by others than the operator normally using them.

'It is an object of my invention to produce an instrument which can be readily adjusted to meet varying circuit conditions resulting from a change in the operating current, line leakage and other factors, while the deviceis in the normal working position on the head of the receiving operator.

Another object of my invention is to produce a sounder of this class which can be read only by the user.

Another object of my invention is to produce a sounder of the class described which sounds to the user substantially the same as an ordinary non-secret type sounder.

A further object of my invention is to produce a sounder of a design which is simple, and inexpensive to construct and maintain.

The above mentioned and further objects and advantages of my invention will be more fully explained in the following description taken in conjunction with the accompanying drawing.

In the drawing, Fig. 1 is a perspective view of the body portion of a case for housing a sounder embodying my invention.

Fig. 2 is a similar view of a sounder embodying my invention, removed from the case, and

Fig. 3 is a similar View of the cap or cover of the case.

Referring more particularly to Fig. 2 reference numeral l refers to a diaphragm, preferably of insulating material, to which the terminals 2 and the sounder base 3 are attached in any well known manner. Numeral 4 indicates a ring of soft resilient material such as felt for holding the diaphragm I out of direct contact with the case l5. On the sounder base 3 are mounted a magnet yoke 5, an anvil 8 and an adjusting lever 12, the magnet yoke 5 carrying the operating magnet 6 and the armature l, the latter being supported on a knife edge 2i or other suitable bearing. The anvil 8 carries a backstop 9 for the armature. This backstop may be formed integral with the anvil 8 or maybe attached thereto as indicated in Fig. 2.

The armature 'l is held in position against sidewise movement on the bearing 2| by a pin !9 rigidly fixed to the magnet yoke 5, and passing loosely through a hole in the armature 1. Guides l formed as a part of the anvil 8 or alternatively as a part of the backstop 9, or even as separate pieces attached either to the anvil 8 or the backstop 9, serve to hold the end of the armature in position between the front and backstops wh no pull is exerted by the retractal spring l latter spring has one end connected to an extension of the armature I and the other end to the adjusting lever I2 which is, in the preferred form, a flat spring having one end secured to the sounder base 3.

When the unit shown in Fig. 2 is positioned in thecase l5 shown in Fig. 1, the terminals 2 fit into jacks l'6 attached to the case, to which the connecting leads for the sounder are joined. The case is preferably of insulating material 5* connecting leads are brought out through a hole in the case, not shown. The construction is such that with the sounder in the case the free end of the adjusting lever I2 is located opposite an adjusting screw l3, by means of which the position of the adjusting lever and the resulting pull or tension exerted by the spring I l on the armature can be varied at will. The screw I5 is mounted in a split bushing M, which exerts sufficient friction on the screw to prevent it from turning ea ly after it has once been set in the proper posit With the sounder in place in the case 65, the resilient ring 4 rests against face 20 of the cafe with the diaphragm contacting the ring l. When the cap H is screwed in place on the case a second resilient ring l8 of felt or the like in the cap serves to hold the outer face of the diaphragm securely in place, these rings effectively preventing the transfer of sound directly from the diaphragm to the case, but-not preventing the sound from emerging through the hole in the cap I'l.

It is desirable that an instrument of the kind just described be suitable for operation over a Wide range of current values and in circuits having varying amounts of leakage. To accomplish this result the spring and the leverage through which it works are designed so that the increase in retractal pull of the spring on the armature as the latter moves from the backstop to the frontstop or anvil, approximately equals the increase in magnetic pull due to the decrease in air gap between the armature and the magnet core. The efiect of this design is that for any given adjustment of spring H, the current required to operate the armature is only very slightly greater than the current at which the armature releases. Thus, by means of a single adjustment, that of changing the pull of the retractal spring II, the sounder can be made to operate on any current value or quality of circuit encountered in the nor mal course of telegraph operation.

While the principle of properly proportioning the strength of the retractal spring to the pull on the armature with varying air gap is here applied to a sounder, it is equally Well adapted for use inthe design of neutral or non-polar relays, therefore, the illustration of this principle in connection with a sounder should not be considered in a limiting sense. 7

The secret sounder described hereinabove is intended for use in a manner similar to a telephone receiver and may be provided with a head band for that purpose,if desired.

While I have described a particular embodiment of my invention for the purposes of .illustration it should be understood 1 that .various modifications and adaptations thereof, may be made within the spirit of the invention as set forth in the appended claims.

What is claimed is:

1. A secret telegraph sounder comprising a case, a flexible diaphragm resiliently supported within said case and a telegraph sounder mechanism mounted on said, diaphragm and out of contact with said case. a

2. A secret telegraph sounder comprising a case, a diaphragm and a cap, said diaphragm being clamped between said case and said cap and separated therefrom by members of resilient material, a magnetic sounder element. carried by said diaphragm, elongated terminals carried by said diaphragm and co-operating jacks attached to said case and adapted to receivesaid terminals.

3. A secret telegraph sounder comprising a flexible diaphragm, a telegraph sounder mechanism mounted on said diaphragm, a spring for adjusting said soundermechanism, a case forenclosing said diaphragm and sounder mechanism and means extending outside of said case for adjusting the tension of said spring, said last named means constituting the sole adjusting means for the sounder mechanism.

4. A telegraph sounder comprising a case having a cap, a diaphragm positionedtherein with one side adjacent to said cap, said cap having a hole adjacent said diaphragm, an adjustable telegraph sounder attached to and supported by the other side of said diaphragm and a single means extending outside said case for adjusting said sounder. q

5. A telegraph sounder comprising asa unitary structure a yoke having a bearing near one end and an anvil at the other end, a magnet mounted on said yoke and positioned between said bearing and said anvil, and an armature supported by said bearing and adapted to cooperate with said anvil, said bearing comprising a knife edge and a pin, said pin passing through a cooperating hole in said armature and serving to prevent sidewise motion of the latter with respect to said knife edge bearing.

6. An electromagnetic device comprising a magnet and an armature and spring means for drawing said armature away from said magnet, said spring being so proportioned and arranged as to exert a retracting 'force increasing with and substantially equal to the increase in magnetic force due to decrease in the air gap as the armature is drawn toward the magnet upon energization of the latter.

'7. A telegraph sounder mechanism for unitary mounting on a diaphragm comprising a magnet and an armature, a bearing contacting said armature intermediate the ends thereof, one of said armature ends cooperating with said magnet and the other of said armature ends having one end of a retractal spring attached thereto, an adjusting lever fixed at one end, and movable at the other end, the other end of said. spring being attached to an intermediate point of said lever, and means for adjusting the position of said movable end of .said lever whereby the tension of the spring as applied to said armature may be varied. 8. An electromagnetic device comprising a magnetic circuit including a magnet and an armature, front and back stops for limiting the movement of said armature relative to said magnet to provide for maximum and minimum air gaps and a spring means for drawing said armature away from said magnet, said spring and said magnetic circuit being so relatively proportioned that said retracting force exerted by said spring increases with elongation an amount substantially equal to. the increasein magnetic force tending to drawsaid armature to said magnet as said air gapis decreased, upon energization of said magnet.

9. An electromagnetic device for operation under varying current conditions comprising a magnetic circuit including a, magnet and anarmature, front and back stops for limiting the movement of said armature relative to said magnets, a spring for drawing said armature away from saidmagnet, anda single adjusting means operable upon said spring for adjusting said electromagnetic device to compensate for varying current conditions, said spring and magnetic circuit being so proportioned relative to each other as to exert a retracting force and a magnetic force, respectively, which are substantially equal for all positions of said armature within the limited range of movement of said diaphragm, upon energization of said magnet.

10. A telegraph sounder comprising a case, a flexible diaphragm resiliently mounted within said case, a pair of terminal projections mounted on said diaphragm, a sounder base mounted upon said diaphragm, and a magnetic sounder element mounted on said sounder base, said sounder base and sounder being mounted out of contact with said case. ERWIN P. BANCROFI'. 

